Remove Pi-specifics from review-profiles (belong on PR #1313)

The Pi reviewer adapter and Pi model lister were mistakenly added here; they live on the stacked review-pi-reviewer branch (PR #1313), which is based on review-profiles and already carries a fuller Pi integration (reviewer + live models + generate). Strip them so review-profiles is the clean general scout feature with no Pi:

• delete pi/reviewer.go, pi/reviewer_test.go, pi/models.go, pi/models_test.go
• drop the pi case + import from launchableReviewerFor
• de-Pi the ModelLister doc comment

#1313 will be rebased onto this to re-add Pi on top.